1. Background of the Invention
The present disclosure relates to semiconductor memory devices and, more particularly, to a method of providing block state information in a semiconductor memory device having a flash memory.
A claim of priority is made under 35 U.S.C. §119 from Korean Patent Application 10-2006-0107556, filed on Nov. 2, 2006, the contents of which are hereby incorporated by reference in their entirety.
2. Description of the Related Art
Memory devices can be generally classified into two broad categories. These categories are volatile memory devices and non-volatile memory devices. Volatile memory devices do not retain their stored data in the event of a power loss. However, non-volatile memory devices retain their data even in the event of a power loss.
A commonly used non-volatile memory device is a flash memory device. In a flash memory device, data is stored in memory cells. Furthermore, transistors generally function as memory cells in flash memory devices. A flash memory device may be programmed with data or data stored in a flash memory may be deleted using different programming and data deletion techniques. For example, a flash memory device may be programmed by use of a tunneling effect. In the tunneling effect, a relatively large positive potential difference is created between a control gate and a substrate of the transistor. This potential difference causes the electrons on the surface of the substrate to be pushed and trapped to the floating gate. These electrons act as a barrier between the control gate and the channel on the substrate, thus increasing the threshold voltage of the cell transistor. Alternatively, a hot carrier effect may be used to program and/or delete data to/from a memory cell.
In either case, as the number of programming and delete operations increase, the reliability of the memory cells (and thus of the memory device) reduces. That is, there is a limit to the number of programming and delete operations that may be performed on flash memory devices without compromising on the reliability of the device. After such a limit is reached, there may be a substantial increase in programming errors on the device.
To counter the effects of having defective memory blocks, flash memory devices use techniques to replace bad memory blocks with reserved memory blocks that are known to be reliable, i.e., good memory blocks. Many of these techniques involve checking the address of a memory block during a read or write operation. If there is an error in the read or write operation, the block is determined to be a bad block and is then replaced by a reserved block which is assigned the same physical address as that of the bad block. A write or read operation of data is then performed through the reserved block.
FIGS. 1 and 2 illustrate a configuration of general flash memory. As shown in FIGS. 1 and 2, a flash memory includes meta blocks, user blocks and reserved blocks.
The meta block is a block that is generally used to store information associated with bad blocks, information associated with reserved blocks, and mapping information. The user block is generally used to store data. The reserved block, as described above, is used to replace a bad block.
Referring to FIG. 1, if blocks 32 and 34 go bad, these are each replaced with reserved blocks 35 and 36. In this case data is not written to or read from blocks 32 and 34. Instead, data is written to or read from blocks 35 and 36. Now, if another block such as block 38 were to go bad, then block 38 would be replaced with a reserved block 40.
However, when all the bad blocks (including the initial bad blocks), are replaced during the operation, that is, when all the reserved blocks are exhausted, the stability of semiconductor memory device can be no longer guaranteed. At this time, in order to maintain the integrity of the data already stored in the device, the semiconductor memory device automatically goes into a write prohibition state or read-only state. At this time, a user realizes that the life of the memory device is over and therefore executes a memory retention procedure such as, for example, a data backup.
While the integrity of stored data can be maintained as described above, there is no procedure to forewarn the user of the memory device that all the reserved memory blocks are about to be used up. If the user were forewarned, he may be able to take other preventive measures rather than just backing up the data. There is therefore a need for systems and methods which provide memory block state information upon receipt of a request from a user.